A single beam aerial work platform

Abstract: A single beam aerial work platform with a base structure (60), top structure (80), and at least three scissor mechanisms (14). The extending means (116) for raising the top structure (80) relative to the base structure (60) is attached between the first or lower scissor mechanism and the third or top scissor mechanism. The extending means (116) are attached by mounting means (100,108) at an offset to the pivot points and structural members of the scissor mechanisms (14). An additional stress reducing beam (90), attached parallel to one of the structural members of the middle scissors mechanism, reduces the horizontal bending stress in the structural members of the scissor mechanisms (14) and the connecting pin loading in the scissor mechanism pins.

Description: The present invention relates to the field of aerial work platforms of the scissors lift type and particular to a a scissors lift comprising: a top structure; a base structure; at least first, second and third scissor mechanisms interconnected between the top structure and the base structure and each having first and second beams and center connecting means pivotally connecting the first and second beams at central portions thereof; an extending means having first and second ends; upper and lower mounting means for mounting the extending means to the scissors lift; and first and second pivot means for pivotally connecting said first and second ends of said extending means to the upper and lower mounting means, respectively; each of said first and second beams having lower end portions and upper end portions; the lower end portions of the first and second beams of the first scissor mechanism being pivotally connected to the base structure; the lower end portions of the first and second beams of said second scissor mechanism being pivotally connected to the upper end portions of the first and second beams of said first scissor mechanism by end connecting means; the upper end portions of the first and second beams of said second scissor mechanism being pivotally connected to the lower end portions of the first and second beams of said third scissor mechanism by end connecting means. Aerial work platforms are often utilized to enable a person to access areas high above reach to install fixtures, perform maintenance, or the like. Unlike a ladder, which must lean against a solid object or have a second set of supports to be free standing, an aerial work platform is self contained, mobile, stable, and provides a large platform surface upon which the user can work. The disadvantages of most aerial work platforms are their physical size both when collapsed and extended and the amount of energy required to activate their extending means to raise the platform to the desired height. A prior art aerial work platform of the scissors lift type comprising the features of the precharacterizing clause of claim 1 is disclosed in EP-A-0 356 761. The extending means of the scissors lift known from EP-A-0 356 761 is a hydraulic cylinder means. One end of the hydraulic cylinder means is pivotally mounted to the base structure whereas the other (upper) end of the hydraulic cylinder means is pivotally mounted to an upper mounting means which is directly fixed to one of the beams of the lower (bottom) scissor mechanism. FR-A-2 385 638 discloses an aerial work platform of the scissors lift type, which comprises scissor mechanisms each having a pair of first beams extending parallel to each other and defining a space therebetween, and a second beam extending in a cross-like manner relative to the first beams through the space between the first beams. A pair of extending means (hydraulic cylinder means) is provided for extending and contracting the scissors lift in the vertical direction, The opposite ends of each extending means are pivotally connected to different scissor beams by means of upper and lower mounting means fixed to the different scissor beams. It is the object of present invention to improve a scissors lift of the type defined in the precharacterizing clause of claim 1 in such a manner that distortion of the beams caused by bending forces during raising of the scissors lift type aerial platform is reduced. To solve this object the scissors lift according to the present invention is characterized in that said lower mounting means are mounted both to the center connecting means of said first scissor mechanism and a first connecting means pivotally connecting one of the first and second beams of the second scissor mechanism to one of the first and second beams of the first scissor mechanism so as to distribute stresses to said center connecting means of the first scissor mechanism and said first end connecting means, that said first pivot means are spaced from said center connecting means of the first scissor mechanism and said first end connecting means, that said upper mounting means are mounted both to the center connecting means of said third scissor mechanism and a second end connecting means pivotally connecting said one of the first and second beams of the second scissor mechanism to one of the first and second beams of the third scissor mechanism so as to distribute stresses to said center connecting means of the third scissor mechanism and said second end connecting means, and that said second pivot means is spaced from said center connecting means of the third scissor mechanism and said second end connecting means. The scissors lift or aerial work platform of the present invention is one of the single scissors type and utilizes only one set of scissor type structures or beams for lifting purposes. This greatly reduces the overall width of the aerial work platform and allows its use in areas where it was previously impossible to locate an aerial work platform because of space limitations. Likewise, its structure is lighter and more compact than traditional two scissors type aerial work platforms. The present invention provides a scissors lift or aerial work platform that requires only one extending means, typically a hydraulic cylinder. Furthermore, because of the unique and novel positioning of the extending means, the amount of work required by said extending means is greatly reduced. The extending means, typically a hydraulic cylinder, is connected between the first scissor mechanism and the third scissor mechanism using offset mounting assemblies. Due to the resulting mechanical advantage derived from the position of each end of the extending means on each mounting assembly, a smaller and more efficient hydraulic cylinder and hydraulic oil pump for raising the work platform may be utilized. According to the the present invention the first and second beams of each scissor mechanism are pivotally connected at center apertures with suitable connecting means, typically a pin. Each pair of beams forming a scissor mechanism has a pair of lower ends below the center aperture with end portions containing second and third apertures and upper ends above the center aperture with end portions containing fourth and fifth apertures. The lower end portions of the beams of the first or bottom scissor mechanism are connected to the base structure. One end is rigidly connected to the base structure by passing a pin through the aperture in the end portion of the beam and through a similar aperture in the base structure. The other beam end is slidably connected to the base structure. The ends of the pin that pass through the aperture in the end portion of this beam slide in a track on the base structure. As the scissors lift aerial work platform is raised or lowered, this first scissor mechanism closes and opens. The pin slides in the track accordingly. The upper end portions of the beams of the first scissor mechanism are connected to the lower end portions of the beams of the second or middle scissor mechanism with pins that pass through the apertures in each members end portions. Similarly, the upper end portions of the beams of the second scissor mechanism are connected to the lower end portions of the beams of the third or top scissor mechanism with pins. Finally, the upper end portions of the beams of the third scissor mechanism are connected to the top structure of the lifting means with a fixed pin and a pin that slides in a track identical to that described in the base structure. Attached to the upper portion of the first or bottom scissor mechanism between a center aperture and an upper aperture and attached to the lower portion of the third or top scissor mechanism between a center aperture and a lower aperture are hydraulic cylinder mounting assemblies (lower and upper mounting means). The mounting assemblies comprise at least one side plate on either side of the extending means. The ends of the extending means, typically a hydraulic cylinder, for extending the top structure relative to the base structure are connected to the hydraulic cylinder mounting assemblies. The points of connection for the extending means are offset from the pins of each pair of scissors mechanisms to produce a mechanical advantage. The design criterion for determining the offset location are the hydraulic pressure required to start raising the top structure, the existing hydraulic pressure when the top structure is at full raise, and the stresses and loads of a stress reducing beam. The additional stress reducing beam runs parallel to one of the structural members (beams) of the second set of scissors mechanism and is connected to the lower pin of the upper hydraulic cylinder mounting assembly and to the upper pin of the lower hydraulic cylinder mounting assembly. The scissors lift aerial work platform according to the present invention is not limited to three sets of beam pairs (three scissors mechanisms). An additional set of scissor beam mechanisms can be attached to the top of the third set. This would in turn increase the maximum height of the aerial work platform. For example, another three sets could be added to double the maximum height. Provided each addition of three sets indudes an additional extending means, the aerial work platform can be extended to any desired height provided structural integrity is taken into consideration. In the following, a preferred embodiment of the present invention is described with reference to the drawings, wherein: Figure 1 is a side elevational view of a scissors lift aerial work platform according to the present invention. Figure 2 is a front elevational view of the aerial work platform. Figure 3 is a cross-sectional view of the base structure of the aerial work platform taken on line 3-3 of Figure 1. Figure 4 is a cross-sectional view of the top structure of the aerial work platform taken on line 4-4 of Figure 1. Figure 5 is a partial elevational view of the base structure of the aerial work platform showing its wheels. The embodiment of the invention will be referred to as 10 and is shown in figures 1 and 2. Referring to figures 1 and 2, the aerial work platform includes a base 60, a scissors lift assembly 14, and a top structure 80. As can be seen in figure 5, the base 60 includes wheels 62 for mobility of the aerial lift platform. Referring to figure 1, the base 60 contains an aperture 64 and a slide track 66. Beam 160 of scissor assembly 14 is pivotally attached to base 60 by pin 32 which passes through aperture 64 and a similar aperture 162 in beam 160. Beam 170 of scissor assembly 14 is slidably attached to base 60. Pin 52, which passes through aperture 172 in beam 170, is slidably engaged into track 66. As scissor assembly 14 expands and collapses, pin 52 traverses in track 66 accordingly. Base 60 and pin 52 are also shown in figure 3. Referring to figures 1 and 2, the top structure 80 also contains an aperture 84 and a slide track 86. Beam 130 of scissor assembly 14 is pivotally attached to top structure 80 by pin 38 which passes through aperture 84 and a similar aperture 136 in beam 130. Beam 120 of scissor assembly 14 is slidably attached to top structure 80. Pin 58, which passes through aperture 126 in beam 120, is slidably engaged into track 86. As scissor assembly 14 expands and collapses, pin 58 traverses in track 86. Top structure 80 and pin 58 are also shown in figure 4. Scissor assembly 14 includes at least 3 sets of pairs of structural members or beams which each form a scissors mechanism. Each pair has a center aperture through which a common pin passes thus forming each scissor mechanism. The pairs of ends of each scissor mechanism are attached to either another pair of ends or to base structure 60 or to top structure 80. The first pair of scissors mechanism is formed by beams 160 and 170 whose center apertures 164 and 174 are pivotolly pinned together by pin 20. The lower ends of beams 160 and 170 are attached to base 60 as described above. The upper ends of beams 160 and 170 are pivotolly attached to the lower ends of beams 150 and 140 by pins 54 and 34 respectively. Pin 54 passes through aperture 166 in beam 160 and aperture 152 in beam 150. Pin 34 passes through aperture 176 in beam 170 and aperture 142 in beam 140. Beams 140 and 150, which are pivotally connected at their center apertures 144 and 154 respectively by pin 22, form the second pair of scissors mechanism. The upper ends of beams 140 and 150 are in turn pivotally attached to the lower ends of beams 130 and 120 by pins 56 and 36 respectively. Pin 56 passes through aperture 146 in beam 140 and aperture 132 in beam 130. Pin 36 passes through aperture 156 in beam 150 and aperture 122 in beam 120. Beams 120 and 130 are pivotally attached at their center apertures 124 and 134 respectively by pin 24. The upper ends of beams 120 and 130 are attached to top structure 80 as described above. The hydraulic cylinder 116 applies a lifting force to the first and third scissor mechanisms through the upper and lower hydraulic cylinder mounting assemblies 100 and 108. The mounting assemblies 100 and 108 comprise at least one side plate mounted on either side of the extending means. Each mounting assembly 100 and 108 has three apertures. Upper hydraulic cylinder mounting assembly 100 lies along side beam 130. Pin 56, which is pivotally connected to beams 130, 140, and 90, passes through aperture 102 of the upper hydraulic cylinder mounting assembly 100. Pin 24, which pivotolly connects beams 130 and 120, passes through aperture 104 in upper mounting assembly 100. The third aperture 106 of upper mounting assembly 100, to which one end of the hydraulic cylinder 116 is mounted, is offset from pin 56 by a predetermined distance and angle. The design criterion which determine the offset dimensions for the location of aperture 106 are the hydraulic pressure that is present at the start of raising the top structure, the hydraulic pressure that exists when the top structure is at full raise, and the stresses and loads of beam 130. Lower hydraulic cylinder mounting assembly 108 is placed along side beam 170. Apertures 110 and 112 of lower mounting assembly 108 fit over pins 20 and 34 respectively. Mounting assembly 108 has a third aperture 114, to which the other end of the hydraulic cylinder 116 is attached, offset from pin 34 by a different predetermined distance and angle. The same design criteria are used to determine the offset location of aperture 114. The cylinder mounting assemblies 100 and 108 provide for reduced distortion of the beams caused by bending forces during raising of the aerial work platform. Hydraulic cylinder mounting assemblies 100 and 108 and beam 90 reduce the load and stress in pins 20, 24, 34, and 56. In addition, cylinder mounting assemblies 100 and 108 are easily replaced when worn and significantly reduce the repair time required when the hydraulic cylinder must be removed for maintenance purposes. An additional beam 90 is used to further reduce side bending caused by hydraulic cylinder loading in the single scissors mechanism beams. This stress reducer beam 90 reduces the horizontal bending forces in the scissors beams by supporting pins 34 and 56 outside of the hydraulic cylinder mounting assemblies 100 and 108. Stress reducing beam 90 not only shares the load from the hydraulic cylinder 116 but because of its placement outboard of hydraulic cylinder 116 it is in a position to carry the forces with very little bending. It also reduces the pin stresses and the pin deflections by changing originally cantilevered pins 34 and 56 into end supported pins 34 and 56. Pins supported at both ends are more rigid and can withstand a greater load. Stress reducer beam 90 carries primarily an axial load and therefore its cross-section area is only one fourth of that of the scissors beams. Stress reducing beam 90 has replaceable bearings on each end. Additional scissor assemblies 14 can be pivotally connected to the third pair of scissors mechanism to increase the maximum height of my aerial work platform. The only limitation is structural integrity of the components. The foregoing is considered as illustrative only of the principles of the invention. Furthermore, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described. While the preferred embodiment has been described, the details may be changed without departing from the invention, which is defined by the claims.

Claims: A scissors lift comprising: a top structure (80); a base structure (60); at least first, second and third scissor mechanisms (120, 130, 140, 150, 160, 170) interconnected between the top structure (80) and the base structure (60) and each having first and second beams and center connecting means (20, 22, 24) pivotally connecting the first and second beams at central portions thereof; an extending means (116) having first and second ends; upper and lower mounting means (100, 108) for mounting the extending means (116) to the scissors lift; and first and second pivot means for pivotally connecting said first and second ends of said extending means (116) to the upper and lower mounting means (100, 108), respectively; each of said first and second beams having lower end portions and upper end portions; the lower end portions of the first and second beams of the first scissor mechanism (160, 170) being pivotally connected to the base structure (60); the lower end portions of the first and second beams of said second scissor mechanism (140, 150) being pivotally connected to the upper end portions of the first and second beams of said first scissor mechanism (160, 170) by end connecting means (34, 54); the upper end portions of the first and second beams of said second scissor mechanism (140, 150) being pivotally connected to the lower end portions of the first and second beams of said third scissor mechanism (120, 130) by end connecting means (36, 56); characterized in that said lower mounting means (108) are mounted both to the center connecting means (20) of said first scissor mechanism (160, 170) and a first connecting means (34) pivotally connecting one of the first and second beams of the second scissor mechanism (140, 150) to one of the first and second beams of the first scissor mechanism (160, 170) so as to distribute stresses to said center connecting means (20) of the first scissor mechanism (160, 170) and said first end connecting means (34), that said first pivot means are spaced from said center connecting means (20) of the first scissor mechanism (160, 170) and said first end connecting means (34), that said upper mounting means (100) are mounted both to the center connecting means (24) of said third scissor mechanism (120, 130) and a second end connecting means (56) pivotally connecting said one of the first and second beams of the second scissor mechanism (140, 150) to one of the first and second beams of the third scissor mechanism (120, 130) so as to distribute stresses to said center connecting means (24) of the third scissor mechanism (120, 130) and said second end connecting means (56), and that said second pivot means is spaced from said center connecting means (24) of the third scissor mechanism (120, 130) and said second end connecting means (56). The scissors lift of claim 1, wherein the extending means (116) is a hydraulic cylinder. The scissors lift of claim 1 or 2, wherein each of said upper and lower mounting means (100, 108) includes: side plates on opposite sides of the extending means (116); each side plate having first, second and third spaced apertures (102, 104, 106, 110, 112, 114) therethrough; said first and second apertures (102, 104, 110, 112) of each plate lying in a center line and receiving an end connecting means (34, 56) and a center connecting means (20, 24) therethrough, respectively; said third aperture (106, 114) of each plate being located a distance from the center line and receiving one of said first and second pivot means therethrough. The scissors lift of any of the preceding claims, further comprising a stress reducing beam (90) extending between and connected to said first (34) and second one (56) of said end connecting means for reducing bending of the scissors lift during extension and retraction of said scissor mechanisms.

Inventors: LEMKE LEE L, LOOMANS THOMAS J, ZIMMER KENNETH J, LEMKE, LEE L., LOOMANS, THOMAS J., ZIMMER, KENNETH J.
Applicants: MAYVILLE ENG CO, MAYVILLE ENGINEERING COMPANY, INC.
Application year: 1994
Main classification: B66F11
IPC codes: B66F11